Linezolid, with the chemical name of (S)—N-{[3-(3-fluoro-4-(4-morpholinophenyl)-2-oxo-5-oxazoline)]methyl}-acetamide, has a structure as shown in Formula (IV)

Linezolid is a novel oxazolidinone-type antibiotic, which is developed by Pharmacia & Upjohn Company (P&U). Linezolid takes effect on the ribosome of bacteria, and inhibits the synthesis of bacterial protein. Linezolid is mainly used in the treatment of bacteremia caused by vancomycin-resistant enterococci (VRE), pneumonia and complicated skin infections caused by methicillin-resistant Staphylococcus aureus (MRSA), and bacteremia caused by penicillin resistant Streptococcus pneumonia (PRSP).
A methyl substitute of (S)-2-(3-(3-fluoro-4-morpholinophenyl)-2-oxo-5-oxazoline) is the key intermediate in the synthesis of linezolid, wherein the structure is as shown in Formula (I). Linezolid can be obtained by treating the intermediate with a deprotective agent followed by acetylation.
At present, several methods for preparing linezolid as follows are reported:
1. WO957271 reports a synthetic route as follows:

This route is relatively long and requires utilization of dangerous agents such as butyllithium, sodium azide and the like. In addition, the cyclization reaction needs a low temperature as −78° C. The subsequent hydrogenation needs a high pressure, which demands high requirements for the equipment used in the course of synthesis. Accordingly, this route is not suitable for an industrial production.
2. CN1772750 reports a synthetic route as follows:

In this route, highly toxic phosgene is used, and sodium azide and high-pressure catalytic hydrogenation are used in the subsequent reactions. This route has high requirement of the equipment and has some potential safety hazards, thus it is not suitable for an industrial production.
3. WO2007116284 reports a synthetic route as follows:

The yields of the first three steps in this method are relatively low, thereby resulting in a rather high cost.
4. US2007032472 reports a synthetic route as follows:

The yield of the first step in this route is relatively low, and an inversion of configuration might easily happen. The ratio of products to isomers is about 85:15, wherein the isomers are difficult to separate and will be brought into the subsequent reactions till the final product (i.e., linezolid), thereby affecting the product quality.